1. Field of the Invention
The present invention relates to a process for producing poromeric synthetic leather, which comprises:
I. producing an essentially nonporous impregnate by impregnating a textile sheet material with an aqueous polyurethane dispersion and drying, and PA1 II. producing a poromeric synthetic leather from the impregnate by subjecting the impregnate to the action of an aqueous solution of a Br.o slashed.nsted base. The present invention further relates to these poromeric synthetic leathers themselves.
2. Description of the Background
Poromeric synthetic leathers should in their property spectrum come very close to that of high grade natural leather varieties, especially suede leather. This applies particularly to properties such as good water vapor permeability, a high tear strength and pleasant haptic properties.
The production of poromeric synthetic leather is common knowledge (cf. Kunststoffhandbuch, Carl Hanser Verlag, Munich, Vienna, vol. 7:Polyurethane, 3rd edition 1993, chapter 10.2.1.4). Prior art processes all produce their synthetic leathers from solutions or dispersions of polyurethanes which contain organic solvents. For example, in the coagulation process, a textile sheet material is impregnated with an organic solution of a polyurethane, optionally in a mixture with a polyurethane dispersion and optionally a polyelectrolyte, and the sheet material thus pretreated is then passed successively through a plurality of baths comprising mixtures of dimethylformamide and water with decreasing dimethylformamide concentration.
One variant of this process, which leads to textile articles having a particularly pleasant, leatherlike hand, is described in JP 09/18 89 75. A polyester web is impregnated with a solution of a thermoplastic polyurethane in DMF/toluene and then treated with aqueous sodium hydroxide solution. The synthetic leather obtained possesses the flexibility of natural leather.
The disadvantage with these processes is that they produce large quantities of waste air or water which contain organic solvents and have to be worked up in a complicated manner.